Handbrake, the video conversion software, isn't available in the standard Ubuntu repositories. But you can add the official PPA and install Handbrake on Ubuntu and Linux Mint that way (and probably Debian). 

Run these commands to install Handbrake on those operating systems:

sudo add-apt-repository ppa:stebbins/handbrake-releases
sudo apt-get update
apt-get install handbrake-gtk

That will install the GUI version of Handbrake. If you also want to install the command line version of Handbrake, do the following:

apt-get install handbrake-cli

And that's all you have to do.